最长无重复字符子串

int lengthOfLongestSubstring(string s) {  int n = s.length();  int i = 0, j = 0;  int maxLen = 0;  bool exist[256] = { false };  while (j < n) {    if (exist[s[j]]) {      maxLen = max(maxLen, j-i);      while (s[i] != s[j]) {        exist[s[i]] = false;        i++;      }      i++;      j++;    } else {      exist[s[j]] = true;      j++;    }  }  maxLen = max(maxLen, n-i);  return maxLen;}